This invention relates to electrical control circuits and more particularly to electrical control circuits particularly adapted for use in burner control systems.
Burner control systems are designed both to monitor the existence of flame in the supervised combustion chamber and to time sequences of operation of burner controls. Safety of burner operation is a prime consideration in the design of burner control systems. For example, if fuel is introduced into the combustion chamber and ignition does not take place within a reasonable time, an explosive concentration of fuel may accumulate in the combustion chamber. The burner control system should reliably monitor the existence of flame in the combustion chamber, accurately time a trial-for-ignition interval, inhibit ignition if a false flame signal is present, and shut down the burner in safe condition whenever a potentially dangerous condition exists. Examples of such burner control systems are disclosed in my U.S. Pat. No. 3,840,322.
Among the considerations in burner control system design are reliability of operation, manufacturing cost, the provision of precise timing cycles (particularly those of short duration), and the nature of the response of the burner control to a flame failure condition after flame has been established, for example, and immediate shut down of the burner system, an immediate attempt to re-establish flame, or an attempt to re-establish flame only after a pre-ignition (purge) interval.